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UNITED STATES PATENT OFFICE.

CHARLES A. summit, on r novrnuncn, nnonn ISLAND.

PROCESS OF RECOVERI'NG TIN FROM TIN-SCRAP.

SPECIFICATION forming part of Letters Patent No.322,15 7,dated July14,1885.

Application filed March23,1585. (Nospecimens) i To all whom it mayconcern:

Be it known that I, CHARLES A. CA'ILIN, of Providence, in the county ofProvidence and State of Rhode Island, have invented a new and usefulImprovement in the Process of Recovering Tin from Tin-Scrap and otherTinned Metallic Surfaces, which improvement is fully set forth in thefollowing specification.

The present invention has for its object the utilization of waste tinnedscrap, old tin, or other tinned metallic surfaces by recoveringtherefrom'the tin in a form capable of commercial use. a

In Letters Patent No. 190,550, granted May 8,1877, to myself and GeorgeF. Wilson, a process of recovering tin is described, according to whichthe scrap to be treated is first sprinkled with common salt (or otherchlo ride) and nitrate of soda (or other nitrate) and then immersed in ahot or boiling solution of caustic soda or potash,whereby the tin isoxidiZed,and uniting with the soda forms a stannate of soda. The tin issubsequently recovered in that form, either by evaporation of thetin-charged solution to a solid mass or by crystallization of thestannate salt. If metallic tin is desired, it is recovered from thestannate salt by smelting. This process is open to the objection thatthe smelting operation necessary for the recovery of metallic tin isvery difficult and expensive, so much so as to prevent its beingcommercially successful, and, moreover,the soda of the stannate is lostin smelting, while the uses of stannate of soda in the arts arecomparatively few, and there is not,therefore,a demand for itsmanufacture on a large scale.

The present invention is an improvement upon the process set forth inthe aforesaid patent, and is designed to overcome the objections pointedout and to recover the waste tin in an available form, either asmetallic tin or as an insoluble stannate.

According to my present process the cans tic alkaline bath is prepared,the scrap sprinkled with nitrate of soda or other nitrate, and treatedin said bath while boiling or hot, as described in the aforesaid patent.In carrying out the present process the addition of the common salt ispreferably omitted. When the charging with tin has reached the der somecircumstances the quicklime may point desired, the boiling of the bathbeing maintained, I add thereto a proper quantity (depending upon theamount of tin in solution) of an oxide or salt capable of, causingprecipitation of the tin in the form of an in-y soluble stannate. Theprecipitant preferably employed for this purpose is lime in the form tbe added directly to the bath. The insoluble a: l

stannate thus procured may be: readily converted by smelting intometallic tin,or may H be converted by subsequent processes into 3 othersalts of tin.

In order that the invention may be fully understood by those skilled inthe artto which I it appertains, I will explain in detail the man norin. which the process is or may be carried out. A caustic alkalineing-point. The strength of the bath may adbath is prepared in suitableboiler and the heat raised to the boilvantageously be aboutl5i13aum. Thewaste tin or scrap is then sprinkled with a suitable nitrate (nitrate ofsoda is preferred) in the proportions of from three to five pounds ofnitrate to every hundred pounds of tin-scrap,

and the charging with tin is carriedou until the solution (the volumebeing maintained with water) has a strength of from 23 to 25 The boilingofthe bath is main tained (though this is not absolutely neces-I sary)and aproportion of lime is added by de-f Baum.

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grees, the amount dependingupon the quan-@ tity of tin to be removed.

Should the bath be l y the excess of carbonate of soda present, anadditional amount of lime may be added to decarbonate y w the bath; butit is preferred ordinarily to keep the quantity of lime-within thesaturating capacity of the tin present, thus avoiding excess of lime inthe precipitate formed.

When the carbonate of sodabecomes asource of trouble, a furtheradditionof lime may be added, after the tin has been removed, todecarbonate the solution, which process being well understood need not beparticularly described.

While the lime, preferably in the form of dry slack-lime, or milk oflime, maybe added to the bath all at once, it is found better l tointroduce it gradually, a little at a time. By this addition the oxideof the tin is taken from the stannate of soda, and uniting with the lime(oxide of calcium) forms stannate of lime, '(stannate of calcium,)which, being insoluble in the liquid, on stopping the agitation falls tothe bottom, leaving the clear solution of soda above. This solidprecipitate is now to be removed to a drainer, either by scooping it outor by drawing off the soda solution and then removingit, or otherwise.By draining it parts with the greater portion of the causticmother-liquor, and may be entirely freed therefrom by washing, thedrainings and Wash-water being returned to the bath.

The tin of the insoluble stannate thus produced may readily be reducedto metallic form by smelting; or it may be converted into other salts oftin for which there is an indus trial use; or if, instead of using oxideof calcium as the precipitant, a metallic oxide or salt be employed thestannate' obtained may, by reduction directly, produce certain valuablealloyssuch, for example, as the metal obtained by reduction of stannateof copper.

It will be seen that by the above process the alkali of the solution, aswell as the tin, is recovered. In fact,'the're is no consumption ofcausti csoda other than that entailed through loss in handling, which,however, will bemore than supplied by the soda acquired from the nitrateused in treating the tinned scrap. Under favorable circumstances thisacquirement may be so great as to necessitate removal of some of thecaustic soda. The bath, therefore, being freed from the tin oxide, maybe reused, after first, if necessary, decarbonating with lime, as beforeexplained. When this deearbonating process is to be carried out, all thetin should first be removed; but otherwise it is not necessary to removeall the tin at any one operation, as there would be no loss incurred byallowing a portion of it to remain.

It is obvious that any of the soluble salts of lime may be employed forthe removal of the tin from the caustic bath by'double decomposition,producing the stannate of lime.

Indeed, it is or may be an advantage to use the nitrate of lime, thusproviding the nitrate for the treating process and the lime base at thesame time; but it will be understood that the invention is not confinedto the use of lime, since any other salt or oxide which will causeprecipitation of an insoluble stannate either by simple reaction ordouble decomposition may be used i nsteadsuch, for example, as those ofthe alkaline earths and metallic oxides and salts. Neither is theinvention confined strictly to the details of procedure and proportionsabove set forth, since modifications other than. those indicated may bemade therein without departing from the spirit of the invention. It ispossible, for example, under certain conditions, to add the precipitantsat the outset, and the stripping of the tin and precipitation of thestannate may thus be attained at the same time. over, that the use oftheimprovement described is not confined to the treatment of a stannatesolution produced in the manner above set forth, but is equallyapplicable to the precipitation of valuable products of tin fromstannate solutions of any kind.

Having now explained the invention and the manner of carrying the sameinto effect, it may be observed, in conclusion, that it has long beenknown as a chemical fact that the alkaline stannates can be decomposedby the alkaline earths-such as lime, for example-but, so far as I amaware, the fact has met with no industrial application, and certainlyhas not been applied in the manner or connection and for the purposes ofthe present invention; and it may also be observed that heretofore'manymethods for recovery of tin from scrap have been proposed in which thetin is to be dissolved and then precipitated, and in some of which limehas been the precipitating agent; but the precipitate has always, so faras I am aware, been an oxide of tin,'and when lime has been used itsoperation is to unite with the acid of the tin compound and go intosolution, the tin precipitating as oxide, whereas in the presentinvention the lime or basic body unites with the tin and is precipitatedalong with it, leaving the solution free.

\Vhat I therefore claim is 1. The process of recovering tin from tinnedmetal, scrap-tin, and the like by dissolving the tininanalkalinebathandprecipitatingittherefrom in the form of an insoluble stannate,substantially as described.

2. The process of recovering both the tin and alkali from a solution ofalkaline stannate by precipitating the tin from the solution in the formof insoluble stannate, leaving the alkali in solution, substantially asdescribed.

3. In the process of recovering waste tin, the improvement consisting indissolving the tin in an alkaline bath and adding to the solution asuitable oxide or salt, (such as oxide of lime,) whereby the tin isprecipitated in the form of an insoluble stannate, substantially asdescribed.

In testimony whereof I have signed this specification in the presence oftwo subscribing witnesses.

CHAS. A. OATLIN. Witnesses:

EDWARD E. DARLING,

COURTLAND W. GILMORE.

It is obvious, more- IIO

